The general and long term objectives of this research program are to investigate molecules essential to retinal function, and to identify and characterization of a retinal glutamic acid rich protein (garp) which was previously identified in bovine rod outer segments copurifying with rod cGMP phosphodiesterase. More recently, garp has been shown to be covalently linked with the second subunit of the cGMP-gated cation channel of bovine rod photoreceptors, making it a candidate gene for retinal disorders. At least one form of Bardet-Biedl syndrome, a systemic disorder of development that includes retinitis pigmentosa, has been linked to the long arm of chromosome 16. Our finding that the human garp gene is localized to the same region leads us to suggest that defects in garp may be involved in the etiology of this disease. To investigate this possibility, the garp gene will first be characterized in the DNA of normal and Bardet-Biedl patients using heteroduplex and single strand confirmation polymorphism analysis. Any point mutations suggested by these assays will be investigated by direct sequencing of PCR fragments. In conjunction with the gene characterization studies, an immunological characterization of human garp will be undertaken to determine if this protein associates with the channel in an analogous manner to bovine garp. Finally, the expression pattern of garp in neonatal and adult mice will be investigated using ribonuclease protection assay and quantitative Western analysis. Successful completion of these experiments will provide valuable insight into molecular basis of a severe form of retinitis pigmentosa, and provide the information necessary to investigate the role of garp in the function of the cGMP-gated cation channel.